Along with the development of more and more local nodes such as Femtocells, microcells and relays, traditional macrocell-based network architecture has gradually evolved into network architecture where various base stations coexist, so as to achieve the network coverage at multiple layers. In order to improve the relevant performances of the network architecture where the various base stations coexist, network architecture for coordination/aggregation among Evolved NodeBs (eNBs) via a non-ideal link has been proposed, and in this architecture, parts of Radio Bearers (RBs) of a User Equipment (UE) are carried on a Master Cell Group (MCG) managed by a Master eNB (MeNB). The parts of RBs include Signaling Radio Bearers (SRBs) and Data Radio Bearers (DRBs). The other parts of RBs of the same UE (including both SRBs and DRBs) are carried on a Secondary Cell Group (SCG) managed by a Slave eNB (SeNB). During the separation of the RBs of the UE, uplink data and downlink data for the UE may be transmitted simultaneously on two eNBs respectively. Due to the imbalance of the uplink and downlink load, merely the uplink data or the downlink data on one RB may be admitted by the eNB in the case of congestion. However, it is impossible for the current admission control to support the eNB to separately admit the uplink data or downlink data on one RB. At this time, both the uplink data and the downlink data on the RB will be rejected.
A bearer separation technology will be described hereinafter briefly.
Referring to FIG. 1, in a possible multi-layered network coverage environment, a non-ideal data/signaling interface Xn (a wired or wireless interface) may be adopted between an MeNB and an SeNB, and the UE may be operated simultaneously at the MeNB and the SeNB. In the case that a UE connected to the MeNB enters the coverage of a cell corresponding to the SeNB, considering a signal intensity or load balance, the MeNB may transfer a part of, or all of, the data/signaling of the UE to the SeNB, so as to acquire services provided by the SeNB, thereby to enable the UE to use resources of the MeNB and the SeNB simultaneously and achieve inter-eNB aggregation. In this scenario, the RBs of the UE may be carried by a cell (MCell) controlled by the MeNB and a cell (SCell) controlled by the SeNB respectively. The RBs transferred to the SeNB may include DRBs and/or SRB. Because the SeNB is controlled by the MeNB, so the SeNB may be considered as a controlled eNB, and the MeNB may be considered as a controlling eNB.
FIG. 2 shows a bearer separation architecture, where the UE may include separate RBs for the MeNB and the SeNB, and include a separate Packet Data Convergence Protocol (PDCP) entity on each eNB. The uplink data and the downlink data for an identical RB may not be transmitted over the MeNB and the SeNB simultaneously.
FIG. 3 shows another bearer separation architecture, where the UE may include separate RBs for the data on the MeNB, and a part of the data carried by an identical Evolved Packet System (EPS) on the MeNB may be transmitted over the SeNB. The PDCP entity carried by the EPS is still included in the MeNB, while a separate Radio Link Control (RLC) entity is included in the SeNB.
For an identical downlink bearer, the MeNB may control whether or not the data is to be transmitted over the SeNB or MeNB, or the quantity of the data to be transmitted (the data distribution for the downlink bearer).
For an identical uplink bearer, the uplink data of the UE may be configured by the network to be transmitted merely by the MeNB or SeNB (i.e., the uplink data may not be distributed), or to be transmitted over the MeNB and the SeNB at a certain proportion (i.e., the uplink data may be distributed over the MeNB and the SeNB). For example, 50% of the uplink data of the UE may be configured by the MeNB to be transmitted over the MCG, while the remaining 50% of the uplink data may be configured to be transmitted on over the SCG.
Radio Admission Control (RAC), as a functional module of each eNB, is used to control the admission or rejection of a request for establishing a new RB. In this regard, the RAC needs to take an entire resource condition at a network side, a Quality of Service (QoS) requirement of the new RB, QoS guarantee provided by an on-going progress, and a priority and system QoS requirement into consideration. The RAC aims to admit the request for establishing the RB and provide corresponding available radio resources, so as to improve the radio resource utilization. In addition, the RAC also aims to reject the request for establishing the RB, so as to ensure the QoS for the on-going progress.
During a handover process, a source eNB may provide a list of Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Radio Access Bearers (E-RABs) to be established to a target eNB in a handover request. Then, the target eNB may admit all of, or parts of, these E-RABs in accordance with its actually-available resources. As shown in FIG. 4, in the case that it is impossible for the target eNB to admit any bearers in the handover request, it may return a handover preparation failure message to the source eNB. As shown in FIG. 5, in the case that the target eNB has admitted parts of, or all of, the E-RABs, it may return a handover request acknowledgement message to the source eNB, and a list of the admitted E-RABs, a list of the rejected E-RABs and a rejection cause may be carried in this message.
During bearer establishment in a non-handover process, as shown in FIG. 6, a Mobile Management Entity (MME) may send an E-RAB setup request message to the eNB during the bearer establishment process, and a list of the E-RABs to be established may be carried in this message. Then, the eNB may admit all of, or parts of, these E-RABs in accordance with its actually-available resources. In the case that the eNB has admitted parts of, or all of, the E-RABs or rejected all of the E-RABs, it may return an E-RAB setup response message to the MME, and the list of admitted E-RABs, the list of the rejected E-RABs and the rejection cause may be carried in this message.
In a word, in the case of bearer separation, one bearer of the UE may be connected to a plurality of eNB simultaneously. In the case that a current eNB is able to merely accept the downlink data or the uplink data, the admission control of the current eNB may reject all the uplink and downlink data on the bearer. As a result, it is impossible to increase a transmission rate at a UE side due to only uplink bearer separation or only downlink bearer separation, so it is impossible to acquire a gain in the load balance at a network side due to only uplink bearer separation or only downlink bearer separation. In the case of a heavy network load, the bearer or UE connection may probably be released.